Electrosensitive recording article and method of making the same



May 26, 1970 D. R. DAVIS F-TAL 3, 1

ELECTROSENSITIVE RECORDING ARTICLE AND METHOD OF MAKING THE SAME FiledNOV. 1'7, 1966 INVENTORS DALE R. DAVIS ROBERT W. Kl NGSTON ATTO R NEYUnited States Patent US. Cl. 117-217 4 Claims ABSTRACT OF THE DISCLOSUREAn improved electrosensitive recording medium and method of making thesame provides a matrix of conductive particles in a cross-linked binderdisposed on a conductive backing layer for improved resistance tosurface abrasion by a surface-contacting writing electrode.

This invention relates to an improved electrosensitive recording mediumwhich responds to low voltage and low power writing signals, and to themethod of making the same.

It is an object of the present invention to provide an improvedelectrosensitive recording medium which provides contrasting marks orrecords in response to applied writing signals and which includes anelectrosensitive surface coating that resists abrasion and mechanicalscraping at elevated recording temperatures by the recording electrodeof recording apparatus.

It is another object of the present invention to provide a method formaking an improved electrosensitive recording medium.

In accordance with the method and means of the pres- 3,514,325 PatentedMay 26, 1970 The thickness of the layer 13 as measured by its resistanceper square should be within this range so that low voltage writingsignals applied through narrow electrodes in contact with the surface ofthe recording medium may attain a sufiiciently high current density tovaporize the aluminum in the contacted area, thereby exposing thebacking material in the regions through which writing signal flowed.Lower resistances per square (i.e. thicker films) require considerablyhigher power to vaporize the aluminum layer in the contacted region andhigher resistances per square (i.e. thinner films) require higherwriting voltages (typically above 60 to 100 volts) to provide sufficientpower to vaporize the aluminum layer Thus, since the limits are notprecise, the term approximately as used herein is intended to covervalues of resistance per square which are as much as an order ofmagnitude away from the expressed limits but which are useful withhigher power, high voltage writing signals. Thus if sufiicientlytransparent backing material 11 is used, a recording 15 on the presentmedium may serve as an optically-transmissive master in inexpensivereproduction or electrooptical reading of the recording medium.

The surface coating 17 is prepared according to one embodiment of thepresent invention as follows: 300 grams of conductive zinc oxide (NewJersey Zinc Co. grade 013 or 016) and 400 grams of tetrahydrofuran ormethylethylketone are combined with 100 grams of an organic polymer suchas Eponol 55B40 (Shell Chemical Co.) and 15 grams of polyisocyanatecross-linking agent such as Mondur CB-6O (Mobay Chemical Co.). Otheruseful combinations of binder materials and crosslinking agents (somebeing aided by a catalyst) are described in Shell Chemical Co., Plasticsand Resins Division, Technical Bulletin SC:6451 and in the following entinvention, a thin layer of aluminum is deposited on table:

Wei ht Ratio Percent cross-linker Disper- C r of Zinc Oxide Cross-linker(by weight Percent s ion pot to Binder Binder Agent of Binder) CatalystCat. life Time Temp. F.)

41 Eponol 551340 1 Toltuene diisocyanmole percent...-. None 0 3 hrs 7days 72 do. 15 mole percent d0 0 4 hrs do 72 Uformite 9 MX61 50 wt.percent -.do. 0 4 days. 24 hrs. 200 do 20 wt percent d0 0 5days 24hrs200 do do I 50 wt. percent p-Tgi uene sulfonic 1 3 days 2 hr 200 30 4:20 wt. percent 200 4: 50 wt. percent. 250 4; 54 do do 0 2 4:1. CYMEL 4245-8 10, 30, 50, wt. percent. p-Ttilclllene sulfonic 1 2-3 days. 200

ac 4:1 -do 1 Mondur B 03450.... 30, 60 Wt. percen N e 0 1, 2 days.lgifiiays 1;?

rs. an Vitel B PE200 do a 10-50 wt. percent .-do--- 0 4 days. 3 wks 723:1; Butvar 76 7 Uformite MX61 20 wt. percent 0 6 days 24 hrs 200 1Shell Chemical Co. 1 Robin and Haas Co. a Union Carbide. 4 AmericanCyanamid. 5 Mobay Chemical Co. Goodyear Rubber & Chemical Co. 1Shawinigan Resins backing material to form a conductive layer having aselected resistance per square unit area. A surface coating includingzinc oxide in a conductive matrix which is bonded together in across-linked polymer binder is provided on the conductive layer to forma recording medium which produces contrasting marks in response toapplied writing signals.

These and other objects of the invention will be apparent from a readingof this specification and an inspection of the accompanying drawingwhich shows electrosensitive medium and recording apparatus according tothe present invention.

In the drawing, there is shown an electrosensitive recording medium 9which may be prepared according to one embodiment of the presentinvention as follows: Aluminum is vacuum deposited or sputtered onto asuitable backing material 11 such as paper or plastic film using wellknown methods to form a thin conductive layer 13 having a resistanceranging from approximately one ohm to approximately one hundred ohms persquare.

The ingredients selected for the surface coating are then finely groundand dispersed in a ball mill operating for several hours. The agitatedmixture forms a dispersion which is then deposited on the aluminum layer13 by suitable means such as reverse roll coating to a dry weight ofabout three pounds per one thousand square feet. The volatile fluids arethen driven oif in a drying oven leaving the conductive particles andbinder in the surface coating 17 about .5 mil thick on the aluminumlayer 13. The coated medium is then baked typically at about 200 F. forfour hours to produce the cross-linking reaction. The binder in theresulting conductive matrix thus includes a three-dimensionallycross-linked polymer which provides a firm bond to the aluminum layerthat does not exhibit viscous flow at elevated temperatures and hencethat resists-mechanical scraping and abrasion at the elevatedtemperatures encountered during recording. This has the advantage overconventional uncrosslinked binders that the residue from the recordedregions is a mere powdery substance which does not accumulate around therecording electrode that contacts the surface of the recording medium.Heretofore, the conventional uncross-linked surface coatings ofelectrosensitive recording media have exhibited substantial viscous flowat the elevated temperatures encountered during recording. There, thesurface-contacting recording electrode scrapes 01f the softened binderwhich thus accumulates around the electrode as gummy globules that buildup and interfere with the electrode contact.

Therefore, the improved electrosensitive recording medium of the presentinvention is capable of producing a contrasting mark in region thereofthrough which electrical recording signal flows without producingsubstantial amounts of gummy rubble or objectionable residue that canbuild up around the surface-contacting recording electrode.

We claim:

1. An electrosensitive recording medium which prior to recordingcontrasting records therein in response to applied electric writingsignals, comprises:

a metal conductive layer on an insulating substrate;

and

a conductive coating matrix on the surface said conductive layer whichis capable of directly producing a contrasting record at elevatedtemperatures associated with electrographic recording thereon, thecoating matrix including conductive particles in a binder which ,is thereaction product of an organic polymer that is capable of formingmolecular cross links and a molecular cross-linking agent that iscapable of interacting with said organic polymer to form molecular crosslinks and which includes crosslinked molecules, whereby the cross-linkedbinder prevents substantial viscous flow of the binder at elevatedtemperatures associated with electrographic recording thereon.

2. An electrosensitive recording medium as in claim 1 wherein saidconductive particles include particles of zinc oxide which are dispersedthroughout said matrix.

3. The method of producing an electrosensitive recording mediumcomprising the steps, performed prior to electrosensitive recordingthereon, of:

forming a surface coating on a conductive hacking by depositing thereona fluid dispersion comprising conductive particles, an organic binderthat is capable References Cited UNITED STATES PATENTS 3,207,601 9/1965Giaimo 96-15 3,411,948 11/1968 Reis 117-217 ALFRED L. LETVITT, PrimaryExaminer C. K. WEIFFENBACH, Assistant Examiner US. Cl. X.'R. 96--1.8;117-218

